Line count kata

LineCount.scala

package lines

import java.io.File
import scala.annotation.tailrec

object LineCount {

  def of(file: File): Int = {
    val source = scala.io.Source.fromFile(file)
    try of(source.toStream)
    finally source.close()
  }

  def of(string: String): Int = of(string.toStream)

  def of(input: Stream[Char]): Int = countLines(input, nonEmptyLines = 0)

  @tailrec
  private def countLines(
      input: Stream[Char],
      nonEmptyLines: Int,
      currentLineIsEmpty: Boolean = true): Int = {

    def newNonEmptyLines: Int = nonEmptyLines + (if (currentLineIsEmpty) 0 else 1)

    input match {
      case Stream.Empty => newNonEmptyLines

      case '\n' #:: remaining => countLines(remaining, newNonEmptyLines)

      case whitespace #:: remaining if Character.isWhitespace(whitespace) =>
        countLines(remaining, nonEmptyLines, currentLineIsEmpty)

      case '"' #:: remaining =>
        countLines(remaining.dropWhile(_ != '"').tail, nonEmptyLines, currentLineIsEmpty = false)

      case '/' #:: '/' #:: remaining =>
        countLines(remaining.dropWhile(_ != '\n'), nonEmptyLines, currentLineIsEmpty)

      case '/' #:: '*' #:: remaining =>
        val commentSize = remaining.sliding(2).takeWhile(_ != "*/".toStream).size + 2
        val (comment, afterComment) = remaining.splitAt(commentSize)
        countLines(
          input = afterComment,
          nonEmptyLines = if (comment.contains('\n')) newNonEmptyLines else nonEmptyLines
        )

      case nonWhitespace #:: remaining =>
        countLines(remaining, nonEmptyLines, currentLineIsEmpty = false)
    }
  }
}

LineCountTest.scala

package lines

import org.scalatest.{FlatSpec, ShouldMatchers}

class LineCountTest extends FlatSpec with ShouldMatchers {

   "Line count" should "have 0 lines for empty files" in {
     LineCount.of("") shouldBe 0
   }

   it should "have 0 lines for lines with just whitespace" in {
     LineCount.of("  \n\t\n\n") shouldBe 0
   }

   it should "count lines with text" in {
     LineCount.of(
       """def fun(arg1, arg2): foo
         |
         |def bar: 3
       """.stripMargin) shouldBe 2
   }

   it should "discard line comments" in {
     LineCount.of(
       """// This file contains 3 lines of code
         |public interface Dave {
         |  int countLines(File inFile); // not the real signature!
         |}
         |
       """.stripMargin) shouldBe 3
   }

   it should "discard block comments" in {
     LineCount.of(
       """// This file contains 3 lines of code
         |public interface Dave {
         |  /**
         |    * count the number of lines in a file
         |    */
         |  int countLines(File inFile); // not the real signature!
         |}
         |
       """.stripMargin) shouldBe 3
   }

   it should "discard bizarre comments" in {
     LineCount.of(
       """/*****
         | * This is a test program with 5 lines of code
         | *  \/* no nesting allowed!
         | //*****//***/// Slightly pathological comment ending...
         |
         |public class Hello {
         |    public static final void main(String [] args) { // gotta love Java
         |        // Say hello
         |        System./*wait*/out./*for*/println/*it*/("Hello/*");
         |    }
         |
         |}
         |
       """.stripMargin) shouldBe 5
   }
 }